This invention relates to an improved tubing hanger and running tool with a preloaded lockdown of the tubing hanger to the wellhead housing which overcomes the disadvantages of prior subsea tubing hangers and running tools.
Tubing hangers are typically designed to support the weight of the associated tubing strings by landing on a seat within the wellhead housing. The tubing hanger is then locked in position by urging a split ring carried on the tubing hanger body into a recess in the wellhead housing interior wall which prevents upward movement of the tubing hanger. Due to manufacturing tolerances and debris which may have accumulated on the landing seat in the wellhead housing during prior drilling operations, it has been necessary to make the recess which the split ring engages longer than the split ring. This additional length allows room for the tubing hanger and split ring to reciprocate within the recess as the tubing string lengths grow or contract due to thermal stresses.
Once the running tool is removed from the tubing hanger and wellhead, residual torsional force exerted on the tubing hanger by the tubing strings suspended below can cause the tubing hanger to rotate with respect to the wellhead housing and move from its original orientation. This loss of orientation can damage or make it impossible to reinstall the running tool during subsequent tubing string operations or install the subsea tree subsequently. As drilling and production technology has allowed such operations in deeper water depths, operators have insisted on the use of metal-to-metal seals to seal the annulus between the tubing strings and the last casing string. These type of metal-to-metal seals are easily damaged by excessive movement after energization. The reciprocating and rotational motions described above are extremely deleterious to these metal-to-metal seals. The present invention overcomes these problems by providing a novel apparatus for preloading the tubing hanger and preventing reciprocating or rotational movement of the tubing hanger.
U.S. Pat. No. 3,693,714 to B. F. Baugh discloses a typical prior art tubing hanger and running tool which utilizes an expansible lock ring to secure the tubing against upward movement with respect to the wellhead housing.
U.S. Pat. No. 4,067,062 to B. F. Baugh is an example of a tubing hanger allowing use of multiple tubing strings and an associated hydraulic running tool which can run and lock the tubing hanger within the wellhead and is releasable therefrom. The running tool can be subsequently reconnected to the tubing hanger and hydraulically unlatch the tubing hanger and retrieve it to the surface.
U.S. Pat. No. 4,067,388 to E. M. Mouret discloses a running tool and tubing hanger combination which allows release of the tool from the tubing hanger by hydraulic pressure or rotation of the running string to which the tool is attached.